Air quality improves, smoke still prevalent

Smoke creeps in Aug. 28 from the south as the air cools in the South Lake Tahoe area. Although wind had pushed the smoke over for a portion of the day, dropping temperatures eventually returned the smoke by night.

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Although smoke concentration from the Rim Fire has decreased and air quality has improved, spikes of “unhealthy” and “very unhealthy” levels continue to be recorded at the South Shore.

At 4:18 p.m. Tuesday, the Rim Fire, located about 60 miles southeast of South Lake Tahoe, was reported to be 235,841 acres, and containment increased from 30 percent Thursday to 75 percent Tuesday, according to Inciweb.org. According to figures provided by the El Dorado Air Quality Management District, South Lake Tahoe had an index of 159, or “unhealthy” air, recorded at 5 a.m. Thursday.

But by 5 a.m. Friday, the levels had receded to 29 on the index meter, or “good” air quality.

Dr. Warren Withers, Barton Health Systems director of emergency medical services in South Lake Tahoe, stated in an email he saw one patient Monday with respiratory issues related to the smoke, whereas in recent shifts he had been seeing three to five patients.

“I think it’s tapering off a bit,” Withers stated in an email.

The highest recorded particulate measurement from Thursday to 5 p.m. Tuesday was 194, almost “very unhealthy” status, at 2 a.m. Sunday. At the air quality index of 200, air is considered to be “unhealthy” and above 300 is considered “hazardous.”

Until 6 p.m. Tuesday, air quality remained at “good” to “moderate” levels and came close to “unsafe for sensitive groups.”

El Dorado County Air Quality Management District representatives Lisa Peterson, engineer, and Candice Thomas, senior air quality specialist, said levels of smoke particulates have decreased on average.

Smoke has concentrated periodically in the South Lake Tahoe area due to a “basin effect,” Thomas said. The air cools down at night and in the early morning, settling down in lower elevations.

Most of the smoke is made up of smaller-size particulates, which can permeate airways in humans, Thomas said.

“You’re basically surrounded by mountains, and it’s leading to a more concentrated effect,” Thomas said. “There’s also the temperature component, so you get an inversion layer.”

Inversion layers occur when hotter air travels higher over a layer of cooler air, typically seen in areas with dramatic altitude change, according to the National Weather Service website.

As far as forecasts of the smoke in the near future, Thomas said the department cannot tell if the smoke will be curtailed in the near future.

“There’s less smoke production than there has been,” Thomas said. “Previously, we were in the ‘hazardous’ (designated air quality), so it’s decreased from that.”

The Rim Fire at one point burned 50,000 acres in a 24-hour period, according to figures from Inciweb, it has been more than a week since the fire burned more than 25,000 in that time frame.

“There’s no way to really know,” Thomas said.

But that doesn’t mean the smoke will or will not die any time soon, Thomas said.

“Fire season isn’t over yet, and there are still concerns of this fire growing or another one starting,” Thomas said.